Prompt recovery of an incapacitated or trapped person, such as a firefighter, requires rapid notification that the person has been trapped or incapacitated, as well as rapid location of the person. To provide notification of incapacitation, a Personal Alert Safety System (PASS) device can be worn by each firefighter; the PASS device detects incapacitation with a motion detector. When no motion is detected for a preset time interval, an alarm signal is generated. Typically, the alarm signal may also be manually triggered by the user. The alarm signal is typically an audible alarm to notify nearby personnel that the user has been incapacitated and to aid in locating the user. The audible alarm may be ineffective for providing notice in high-noise environments or if the responding personnel are distant from the user, and U.S. Pat. Nos. 4,959,637 and 5,045,839 teach PASS devices which send a radio signal to a remote location to provide notice of incapacitation. The '637 device transmits a coded radio signal which identifies the incapacitated person. Even these radio-signaling PASS devices rely on an audible alarm that is associated with the person to aid in locating the incapacitated person, which may slow or defeat recovery in high-noise environments.
U.S. Pat. No. 4,468,656 teaches a system which uses radio signals to locate a downed person, each individual having a radio transmitter which activates in the event that no motion is sensed for a predetermined period of time. It does so, in part, by having each party on a separate radio frequency and then having a separate receiver that can search for the individual whose transmitter is activated. The receiver must be switched to the particular frequency of the activated transmitter, and directs a rescue party to the individual by using multiple antennas and triangulating to obtain a search direction and distance reading. Once the individual has been reached, the receiver can be switched to track locator transmitters to enable the search/recovery team to locate an exit. This system, while an improvement, still results in considerable delay time until the party can be reached, since searches must be sent in from the outside. The system also does not allow individuals to locate an exit route unless they have been reached by the rescue team. The system also employs a high intensity lamp and an audio generator on each transmitter device, suggesting that the radio direction finding technique taught in the '656 patent may be limited in its ability to precisely locate an individual transmitter.
U.S. Pat. Nos. 6,504,794 and 6,826,117 teach a system which provides similar functions to the system of the '656 patent, but which employs ultrasonic signals rather than radio signals. These patents point out that RF triangulation requires frequencies in the range of 10 GHz or higher, and that such radio frequencies are susceptible to reflection and attenuation by common building materials. Using the system taught in these patents, an ultrasonic beacon is activated either manually or in response to detection of a no-motion condition when a firefighter is incapacitated or in need of assistance. The rescue team can then use an ultrasonic tracking device which receives the signals from the beacon to locate the individual. Again, transmitters can be placed at exits or other safe locations to allow the rescue team to locate an exit once they have recovered the individual. While the system taught in these patents may offer many benefits, the resulting system is extremely complex and may be difficult to implement. In fact, the '117 patent teaches that the noise from a fire may cause interference at the frequencies typically employed for ultrasonic devices. The '117 patent teaches filtering to overcome such interference, further complicating the system.
Avalanche transceivers have been worn by skiers and other persons in areas subject to avalanches to allow rapid and precise location of persons buried by avalanches. These devices are worn in a transmit mode, where they transmit a modulated electromagnetic signal at a specified frequency. If the user is buried by an avalanche, a rescuer using a similar device in a receive mode can track the transmitted signal to quickly locate the buried person. If there are multiple burials, the multiple signals from the buried transmitters increase the difficulty of finding the buried persons. Moreover, when there are multiple users in the vicinity of the avalanche, all non-buried persons must take their devices out of the transmit mode to avoid confusion with the signals from the buried persons. This would be the natural response of non-buried skiers, since all able parties in the area would be dedicated to searching for the buried person(s), and thus would switch their transceivers to the receive/search mode. Such transceivers may also be capable of tracking marker transmitters, which are typically placed on the skis of the user to allow locating the skis after an avalanche. One such transceiver is the Ortovox “F1 Plus”, described in a company catalog published in January, 1996. This catalog also offers “Ski Maus” marker transmitters to be used to locate skis lost by skiers.
More recently, this technology has been offered for use by firefighters under the name “Tracker FRT”, using a transceiver based on the transceiver described in U.S. Pat. No. 6,167,249. The transceivers can be used in combination with transmitting markers at the exits to help a disorientated firefighter find his/her way out of a building. However, in the case of firefighters, there are frequently many parties in the region of the downed or disorientated person who would have their transceivers in the transmit mode. Unlike recreational users such as skiers, the primary concern of such firefighters is to fight the fire, not to search for other parties who may be in trouble. Typically, a separate team is assigned to the recovery of injured or trapped firefighters. Thus, in order to avoid the problems of multiple transmitted signals, the operating method of the Tracker FRT system requires the coordination of all firefighter activities so that the active firefighters switch their devices out of the transmit mode when instructed. This instruction must be supplied to the active firefighters and will distract them from their primary responsibility of fire fighting, and can delay the search while the instruction to switch the transceivers is communicated. Additionally, any marker transmitters placed at exit locations to allow a disoriented user to find the exit should be turned off when searching for a person. With the Tracker FRT system, these problems are further exacerbated since the transceivers used automatically switch from the receive mode to back the transmit mode after a period of time. Furthermore, these devices do not provide notice of incapacitation, and thus should only be used in conjunction with a PASS device.
Thus, there is a need for a device which can provide notice of incapacitation as well as aid in quickly and precisely locating the incapacitated person without reliance on an audible or visual alarm, and which can do so when multiple devices are in use.